BEAM-SWITCHABLE TEXTILE ANTENNA FOR WIRELESS BODY AREA NETWORKS (WBAN)
by
MOHD ILMAN BIN JAIS (1130810633)
A thesis submitted
In fulfillment of the requirements for the degree of Master of Science (Communication Engineering)
SCHOOL OF COMPUTER AND COMMUNICATION ENGINEERING UNIVERSITI MALAYSIA PERLIS
2014
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UNIVERSITI MALAYSIA PERLIS
NOTES : * If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentially or restriction.
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√
MOHD ILMAN BIN JAIS 7 JANUARI 1986
SWITCHABLE-BEAM TEXTILE ANTENNA FOR WIRELESS BODY AREA NETWORKS (WBAN)
860107-10-5583 DR. MOHD FAIZAL JAMLOS
2013/2014
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Specially dedicated to my beloved parents, brothers, sisters and friends
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ACKNOWLEDGEMENT
“You simply will not be the same person two months from now after consciously giving thanks each day for the abundance that exists in your life. And you will have set in motion an ancient spiritual law: the more you have and are grateful for, the more will be given you.” -Sarah Ban Breathnach-
Alhamdulillah, thanks to Allah SWT
There are many individuals whom I would like to thank for their support and guidance that made it possible for me to successfully complete this master of science research work . First of all, my sincere gratitude goes to my beloved family, to my beloved parents for giving me life in the first place and for unconditional support and encouragement to pursue my studies in master by research.
The special thank goes to my both helpful supervisor, Dr Faizal Jamlos and Pn.
Shahadah Ahmad. The supervision and support that they gave truly help the progression and smoothness of my research work. The co-operation is much indeed appreciated and I am so honored to have both of you as my supervisors.
Lastly, I would like to express my gratitude to all my colleagues especially Muzammil Jusoh, Thennarasan Sabapathy, Iszaidy Ismail and those who work together to complete the final research work.
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v ABSTRAK
Kerja kajian di dalam tesis ini menumpukan kepada kawalan radiasi tekstil antena berfungsi kepada aplikasi rangkaian kawasan badan tanpa wayar (WBAN). Idea kawalan radiasi tekstil antena ini membantu untuk penghasilan antena yang lebih kecil, penjimatan kos penghasilan dan lebih fleksibiliti. Kawalan radiasi antenna sangat praktikal dalam perbangunan pesat sistem komunikasi tanpa wayar. Kelebihan yang ada pada kawalan radiasi tekstil antena adalah dapat membantu dalam mengelakkan masalah berkaitan penyamaran saluran yang ditanggung oleh pergerakan atau perubahan arah pemakai. Tesis ini memperkenalkan satu kawalan radiasi tekstil antena (BSTA) yang unik dengan keupayaan kawalan radiasi menggunakan frekuensi radio (RF) PIN diod litar pincangan sebagai mekanisma kawalan. BSTA merupakan usaha pertama yang memperkenalkan antena kawalan perambatan radiasi yang boleh dipakai dengan mengeksploitasi pelekat berasaskan perak untuk penyediaan penyambungan antara tekstil dan litar RF. Empat PIN diod suis di diintegrasi ke shildit super BSTA yang simetri. BSTA berupaya mencapai kecodongan radiasi ke arah ±16° dengan puncak pengarahan simulasi dan diukur masing-masing 6.8 dBi dan 6.69 dBi. Antena ini mampu mengekalkan galangan masukan 50 Ω pada frekuensi 2.45 GHz tanpa menggunakan pengubah suku gelombang tambahan.Dengan dimensi 88 x 88 mm2, ia adalah cukup kompak untuk disepadukan dengan pakaian untuk aplikasi WBAN.
Berdasarkan penilaian awal kadar penyerapan tertentu SAR, penyelidikan ini mengesahkan bahawa BSTA adalah selamat kepada tubuh manusia dengan hasil keputusan simulasi SAR kurang daripada 1.6 W/kg dan 2 W/kg untuk setiap 1g and 10g isipadu tisu di bahagian badan tertentu berdasarkan peraturan ICNIRP. Dengan semua keupayaan ditunjukkan dan dibincangkan, BSTA mempunyai potensi besar untuk merealisasikan antena untuk pakaian pintar yang baru.
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vi ABSTRACT
The research work in this dissertation focuses on beam-switchable textile antenna for wireless body area network (WBAN) application. The idea of beam-switchable textile antenna helps to reduce the antenna size and more flexible. Beam-switchable antenna is useful in the rapid growth of the wireless communication system. The advantage of beam-switchable antenna is to avoid the associated signal equalization problems that are incurred as the wearer moves or turns. This dissertation proposed a novel beam- switchable textile antenna (BSTA) with reconfigurable ability which uses Radio Frequency (RF) PIN diodes biasing circuit as the switching mechanism. BSTA is the first effort in realizing a combination of such beam-switching feature onto a wearable radiator by exploiting silver loaded epoxy adhesive to provide a solderless connection between conductive textiles and the RF circuits. Four PIN diode switches are integrated into shieldit super of symmetrical BSTA designed. The BSTA is capable to achieve beam steering ±16° with peak simulated and measured directivities of 6.8 dBi and 6.69 dBi, respectively. The antenna maintains input impedance approximately 50 Ω at 2.45 GHz without the use of additional quarter wavelength transformers. With dimension of 88 x 88 mm2, it is compact enough to be integrated in clothing for WBAN applications.
Based on preliminary assessment of specific absorption rate (SAR) results, this research confirms that BSTA is safe to the human being where the simulation SAR result is less than 1.6 W/kg and 2 W/kg for 1g and 10g mass of tissues correspondingly at particular body parts based on ICNIRP regulation. With all capabilities demonstrated and discussed, the BSTA antenna has big potential in realizing a new smart garment antenna.
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DECLARATIONS...ii
DEDICATION...iii
ACKNOWLEDGEMENTS...iv
ABSTRAK...v
ABSTRACT...vi
TABLE OF CONTENT...vii
LIST OF FIGURES...x
LIST OF TABLES...xiv
LIST OF SYMBOLS & ABBREVIATIONS...xv
LIST OF APPENDICES...xvii
CHAPTER 1 : INTRODUCTION 1.1 Introduction...1
1.2 Problem Statement...3
1.3 Objectives...4
1.4 Scope of work...4
1.5 List of Contributions...6
1.6 Thesis Outline...7
CHAPTER 2 : LITERATURE REVIEW 2.1 Introduction...9
2.2 Introduction to Microstrip Patch Antenna...10
2.3 Wearable Antenna...11
2.3.1 Materials of Wearable Antenna...12
2.3.2 Wearable Antenna Positioning Analysis...14
2.4 Wireless Body Area Network (WBAN)...15
2.5 Reconfigurable Antenna...19
2.5.1 Reconfigurable Antenna Switch Technology...19
2.5.2 Reconfigurable Radiation Pattern Antenna...21
2.6 Soldering Materials...26
2.7 Specific Absorber Rate (SAR)...28
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CHAPTER 3 : METHODOLOGY
3.1 Introduction...31
3.2 Flow Chart Diagram...32
3.3 Requirement of Studies...33
3.3.1 Design Specification...33
3.3.2 Dielectric Materials and Electronic Textile (E-textile)...34
3.3.3 Feeding Technique...36
3.4 Design of antenna using CST...37
3.5 Fabrication Process of the antenna...38
3.6 Measurement Setup...39
3.7 Summary...43
CHAPTER 4 : DESIGN, OPTIMIZATION AND FABRICATION OF BEAM-SWITCHABLE TEXTILE ANTENNA (BSTA) 4.1 Introduction...45
4.2 Design Structure and Operation mode of Beam-Switchable Textile Antenna (BSTA)...47
4.3 Parameter Optimization of Beam-Switchable Textile Antenna (BSTA)...49
4.3.1 Optimizing radius of outer circle (RI)...50
4.3.2 Optimizing radius of center circle (RO)...42
4.3.3 Optimizing width of ring gap (L)...55
4.3.4 Optimizing width of ring (W)...58
4.4 Modified Design Structure of Beam-Switchable Textile Antenna (BSTA)...60
4.5 Result and Analysis...63
4.5.1 Reflection Coefficient...63
4.5.2 Radiation Pattern...64
4.5.3 Surface Current Distribution...66
4.6 Outdoor Measurement...67
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4.7 Preliminary Assessment of Specific Absorption Rate (SAR)...68
4.7.1 Human Model...69
4.7.2 Result and Discussion...71
4.7.3 Analysis of SAR Results...73
4.8 Summary...75
CHAPTER 5 : CONCLUSION AND FUTURE WORK 5.1 Conclusion of Project...76
5.2 Future Work...77
REFERENCES...79
APPENDIX A Publications...91
APPENDIX B Exhibitions...92
APPENDIX C Antenna Parameters Measurement...93
APPENDIX D Data Sheet of ShieldIt Super...95
APPENDIX E Data Sheet of Silver Loaded Epoxy...96
APPENDIX F Data Sheet of PIN Diode BAR50-02v...98
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LIST OF FIGURES
Figure
2.1. Rectangular Microstrip Patch Antenna...10
2.2. Various of wearable antenna for military...12
2.3. Peak 10g SAR level on various human body area with different antenna orientation and antenna positioning ...15
2.4. Organisation of IEEE802.15 Wireless Personal Area Network (WPAN) Group...16
2.5. Construction of the PIFA...17
2.6. Possible placement of the PIFA...14
2.7. Fabricated textile patch antenna placed on the human chest...18
2.8. Radiation patterns of the fabricated textile patch antenna placed on the human chest...18
2.9 Schematic diagram of PIN Diode switches...20
2.10. The reconfigurable Vee-dipole antenna...22
2.11. Simulation monopole circular array antenna (a) Radiating elements (b) Feed line...23
2.12. Fabricated monopole circular array antenna (a) Radiating elements (b) Feed line...23
2.13. Beam shape radiation pattern of monopole array antenna (a) 3-D (b) Polar plot...24
2.14. The photograph structure of a U-slot single patch antennas ...25
2.15. Polar plot radiation pattern of U-slot single patch antenna ...25
2.16. UWB Transparent Antenna...27
2.17. Reflection Coefficient S11 Result of UWB antenna with copper pad and without copper pad. (a) Simulated (b) Measured...27
2.18. Complete model used for SAR evaluation on human head. (a) SAM phantom head (b) Human head SAR level...30
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2.19. (a) Computed the SAR distributions at 2.2 GHz (b) SAR distribution of the
antenna located around the limb of the human body...30
3.1. Overall Flow Chart of the entire project ...32
3.2. Photo of ShieldIt Super ...35
3.3. Silver loaded conductive adhesive...36
3.4. Coaxial Feeding Technique. (a) Structure of Coaxial Probe, (b) Front view of position Coaxial Probe, (c) Side view of Coaxial Probe...37
3.5. Parameter sweep menu by CST...38
3.6. Work flow of fabrication process ... ...39
3.7. S11 (Reflection coefficient) measurement test setup...39
3.8. The radiation pattern measurement system...40
3.9. The outdoor practical measurement schematic setup...41
3.10. A screenshot of the power analysis software interface...42
4.1. Simulated structure of proposed BSTA. (a) front view (b) rear view ...48
4.2. Simulated S11 result with value of RI variance for each "ON" switch state: (a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’ state...50
4.3. Polar Pattern with value of RI variance for each "ON" switch state: (a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’ state...51
4.4. Simulated S11 result with value of RO variance for each "ON" switch state: (a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’ state...53
4.5. Polar Pattern with value of RO variance for each "ON" switch state: (a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’ state...54
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4.6. Simulated S11 result with value of L variance for each "ON" switch state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
state...56 4.7. Polar Pattern with value of L variance for each "ON" switch state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
state...57 4.8. Simulated S11 result with value of W variance for each "ON" switch state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
state...58 4.9. Polar Pattern with value of W variance for each "ON" switch state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
state...59 4.10. Simulated structure of modified BSTA. (a) front view (b) rear view ...61 4.11. (a)Schematic diagram of PIN Diode switches
(b) RF switches integration into BSTA structure...62 4.12. Pictures of the fabricated BSTA. (a) front view and (b) rear view...63 4.13. Reflection Coefficient of the BSTA :(a) Simulated result, (b) Measurement
result, (c) On-body S11 result, (d) On-body S11 measurement setup ...64 4.14. Simulated and measured and radiation polar patterns of the BSTA.
(a) Simulated. (b) Measured...66 4.15. Simulated BSTA radiation patterns for each switch in the "ON" state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
state...66 4.16. Surface currents generated on the BSTA for each switch in the "ON" state:
(a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific "ON" state, all other unmentioned RF switches are in the ‘OFF’
State...67 4.17. Received power of proposed BSTA at various distances...62 4.18. HUGO human body model in CST Microwave Studio (CST MWS)...69
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4.19. Position of proposed BSTA on HUGO human body model : (a) Chest,
(b) Back, (c) Right Arm and (d) Left Arm...71 4.20. Simulated SAR result at 2.45 GHz for 1g and 10g Mass Tissue with
variance location of BSTA for each "ON" switch state: (a) switch (i), (b) switch (ii), (c) switch (iii), and (d) switch (iv). At each specific
"ON" state, all other unmentioned RF switches are in the ‘OFF’ state...72 4.21. Layer of human anatomy...73
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LIST OF TABLES
Table
2.1. Summary of Simulated Antenna Performance...13
2.2. Summary of Simulated Refection Coefficient S11 result...14
2.1. Summary of Measured Antenna Performance...26
3.1. Design Specifications...33
3.2. Parameters of Conductive Textiles ...34
4.1. BSTA performance for different RF switch configurations with value of RI variance...52
4.2. BSTA performance for different RF switch configurations with value of RO variance...55
4.3. BSTA performance for different RF switch configurations with value of L variance...57
4.4. BSTA performance for different RF switch configurations with value of W variance...60
4.5. BSTA performance for different RF switch configurations...65
4.6. Thermal conductivity data for specific tissues for human body at 2.45 GHz...70
4.7. Summary of SAR rate on human body model at 2.45 GHz...74
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LIST OF SYMBOLS & ABBREVIATIONS
θ
ThetaГ
Reflection CoefficientΠ
PiΩ
Ohmη
Efficiencyε
PermittivityΔ
Loss TangentCAD Computer Aided Design
CST Computer Simulation Technology
dB Decibel
dBm Decibel of Measured power referenced to 1 mille watt (mW)
GHz Giga Hertz
ICNIRP International Commission on Non-Ionizing Radiation Protection ISM Industrial, Scientific and Medical
km Kilometer
mm Millimeter
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PAN Personal Area Network
PCPTF Pure Copper Polyester Taffeta Fabric
RF Radio Frequency
SAR Specific Absorption Rate
SNR Signal Noise Ratio
VSWR Voltage Standing Wave Ratio
WBAN Wireless Body Area Network
WLAN Wireless Local Area Network
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LIST OF APPENDICES
Appendix A Publications...86
Appendix B Exhibitions...87
Appendix C Antenna Parameters Measurement...88
Appendix D Data Sheet of ShieldIt Super...91
Appendix E Data Sheet of Silver Loaded Epoxy...92
Appendix F Data Sheet of PIN Diode BAR50-02V...94
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CHAPTER 1
INTRODUCTION
1.1 Introduction
Nowadays, microstrip antenna is among the popular types of antenna used by the researcher. Modern wireless communication systems demand antenna designs with light weight, small size, high frequency operation, and good transmission efficiency. In such a scenario, microstrip antenna offers many unique and attractive properties such as low profile, light weight, compact, conformable structure and easy to fabricate (D.
Misman et al., 2007; D. Misman et al., 2008). In past few decades, microstrip antenna has been widely used in radio systems for various applications such as Bluetooth technology.
Conventionally, microstrip antenna used material type of FR4, which is not flexible. Such material does not fulfill the flexibility requirement to be used as the wearable on-body antenna. In that case, a separate bulky device has to be located on a suitable location of the user body such as leg, hip or thigh and a belt might be required to hold the antenna. In contrast, facilitated with wearable and flexible material such as electronic textiles (e-textiles), a new type of microstrip antenna is developed in this
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dissertation where the main features of wearable antenna are light and flexible.
Moreover, such antenna could be sewed together with the cloth of the user. The principal requirement for wearable antennas is the use of flexible materials for ease of integration into clothing (A. M. Mantash, A. -C. Tarot, S.Collardey, & K Mahdjoubi, 2012; M. A. R. Osman, M. K. A.Rahim, N. A.Samsuri, H. A. M. Salim, & M. F.Ali, 2011; N. H. M. Rais, 2009). With the advancements and availability of various flexible materials, it is now possible to realize such implementation of on-body antenna.
Recent works on on-body antenna are mainly focused on the implementation of directional antenna or omni-directional antenna. However, in practice with the mobility of a user, such antenna will fail to maintain a good signal reception. Various factors such as gain, polarization and directivity will affect the signal reception of this wearable antenna. In this kind of scenario, a reconfigurable antenna could be a good solution where, the antenna could reconfigure its beam, polarization and gain to sustain good reception. In past few decades, reconfigurable antenna has attracted much attention in wireless communication systems such as cellular-radio system, airplane radar, smart weapons protection and point-to-point propagation. Electronic beam-forming with RF switching can be used to enhance spectral efficiency as well as reduces the problems associated with multipath propagation. Beam switching can adjust its pattern so that the main beam always points to particular angle. However, the development of this reconfigurable antenna is mainly focused on inflexible material such as FR4 as mentioned earlier. In this dissertation, a comprehensive treatment will be given on the possibility to develop the reconfigurable antenna using flexible material.
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The aim of this project is to design a wearable antenna with reconfigurable scheme. In order to enable reconfigurable ability, a beam-forming circuit needed to be embedded on textile antenna. Hence, utilization of silver loaded epoxy adhesive has been discovered to provide a solderless connection between embedded beam-forming circuit and the e-textiles.
The antenna is designed using Computer Simulation Technology (CST) Microwave Studio Suite software. The proposed switchable-beam textile antenna fabricated with a substrate made of Felt with permittivity and thickness is 1.22 and 2 mm respectively. ShieldIt super with conductivity of 5.57 x 105 S/m and thickness of 0.15 mm deployed as conductive textile (E-textile). The fabricated antenna will be measured and compared with the simulation result to prove the novel wearable antenna is capable to switch its beam through certain configuration of RF PIN diode.
1.2 Problem Statement
The development of on-body textile antenna application is still in its infancy, mainly delimited by on body- detuning. Additionally, in a body-worn antenna implementation, one needs to be not only concerned with the peak directivity offered by the antennas chosen, but also how this coverage is distributed around the body (P. J.
Soh, G. A. E. Vandenbosch, S. L. Ooi, & M. R. N. Husna, 2011). Operationally, it is important to maintain good antenna directivity (dBi) over most of the whole body to help in avoiding problems with excellent directivity (dBi) over some regions while having very deep nulls in other regions and the associated signal equalization problems that are incurred as the wearer moves or turns. Reconfigurable or switchable technology
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might be one of the solution as it can control radiation patterns according to the movement of users. However, integration of RF biasing circuit components with the textile require investigation to define suitable materials as the soldering iron could not be deployed on wearable textile antenna. Manual stripping technique are invented by (Sang-Jun & Chang-Won, 2011) needed three antenna design to realize reconfigurable- beam wearable antenna. The main challenges in dissertation is to realize single switchable-beam wearable antenna with intergration RF switches on antenna itself for WBAN application.
1.3 Objective
The main aim of the research work presented in the thesis is to investigates and analyze the possibility of introducing reliable reconfigurable scheme on wearable antenna. The main objectives of the study include:
i. To design and evaluate a single wearable beam-switching antenna using conductive textiles.
ii. To implement suitable materials that capable to intergrate the RF switches itself on single wearable beam-switching antenna.
iii. To investigate the reliability and effect of the new beam-switchable textile antenna when operating on a human body.
1.4 Scope of work
The scope of this research consists of several stages to achieve the objectives of this project. The stages are divided into five stages as follows:
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5 Stage 1: Literature Review
Revision and analyze previous research related to wearable textile antenna and reconfigurable antenna to generate new ideas on how to improve their previous works.
An inventive antenna design with the capability of wearable, flexible and reconfigurable beam design will be prioritized.
Stage 2: Analytical Calculation
In order to determine dimension of patch wearable antenna, analytical calculations are carried out based on basic equation of microstrip patch antenna. Based on the microstrip patch antenna , SAR equation is analyzed as well.
Stage 3: Simulation antenna design and optimization
The initial project is started by identifying suitable material for wearable antenna in terms of flexibility and wearable ability. Then, a single patch wearable antenna is designed followed by beam-switching textile antenna. All simulation assisted by CST software. In this stage, beam-forming integrated circuit on simulation using copper strip line is presented. Optimization has been conducted to obtain antenna performance results such as reflection coefficient S11, gain and directivity.
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6 Stage 4: Fabrication and Measurement
Fabrication of prototype wearable antenna using ShieldIt Super as electronic textile (E-Textile) and Felt as substrate is carried out at this stage. The beam-forming circuit is attached on wearable antenna using silver loaded epoxy adhesive. All prototypes are tested and measured in Antenna and Microwave lab (Amrellab) in Universiti Malaysia Perlis (UniMAP).
Stage 5: Assessment of specific absorption rate (SAR)
Wearable antenna is significantly related with specific absorption rate (SAR) analysis. SAR analysis could investigate on-body, in-body and off-body systems. The simulation on-body is done to detect the effect of radiation from the proposed wearable antenna towards human body. Analyses of SAR results ensured the beam switchable textile antenna is safe to human being and environment.
1.5 List of Contributions
The main contributions of the research work presented in this thesis include:
i. Developed a novel single novel switchable-beam textile antenna with beam- steering tilt angle ±16° at theta 0° and 90° respectively.
ii. Deploying a silver loaded epoxy to intergrate the RF switches on single wearable beam-switching antenna itself.
iii. Providing preliminary analysis of switchable-beam textile antenna on human body through Specific Absorption Rate (SAR) results is ≤ 1.6 for 1g and ≤2 for 10g respectively.
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